Lightweight pallets are rarely, if ever used in industrial commerce except in forms requiring substantial departures from the predominant fork lift mode of handling. Consequently lightweight pallets, in forms known prior to the invention, except as specified below, are oftentimes distinguished as slip sheets rather than true pallets. These designs typically embody one or more plastic or corrugated paper sheets that are almost always planar in design. Examples of such pallets or slip sheets are exemplified, for example, in U.S. Pat. Nos. 2,328,397, 3,776,145, and 3,790,010 and French Pat. No. 2,094,046.
The disadvantages of such designs are, of course, apparent and well recognized since modified fitting mechanisms, and fork lift attachments are required for utility.
Progress toward an improved lightweight pallet simulating more closely the utility of heavy duty pallets, such as of wood is described in U.S. Pat. application Ser. No. 684,046, filed May 7, 1976, by E. L. Greenawalt. The principle taught in the Greenawalt design is based on the construction of a lightweight tray that is unitized with the load through a film or equivalent wrapping. The combination of the lightweight tray and a proper film wrapping has been discovered to have surprising bottom fork lift capability.
The present invention is a further improvement on the Greenawalt type of pallet structure, designed to give properties closely simulating a true rigid pallet, but formed of lightweight relatively inexpensive materials, such as by rapid sheet thermoforming techniques.
The invention is particularly the discovery, and disclosure of the feasibility of an especially lightweight, sheet thermoformed pallet embodying the highly distinguishing feature of a raised platform, in conjunction with open spaces underneath the platform for insertion and retrieval of a conventional lifting fork mechanism. For example, a lightweight thermoplastic sheet of between 50-80 mils thickness may be thermoformed to the pallet design disclosed below and used with loads up to 2500 pounds. Such pallets may be used even in conjunction with the difficult case of palletized bags, and stacked several pallets high, while maintaining suitable utility for moving and relocating the stacked pallet loads. Hence, the weight supported suitably on the lowest pallet of the invention is an amazing 5000 lbs.
The preferred but not required mode of use of the inventive pallet enlists the use of traditional pallets (heavy duty), on which the pallets of this invention are supported for warehouse functions. The inventive pallets, however, are beneficially used solely in the shipment mode. Thus, for unloading and loading a boxcar or truck, the pallets may be used in the fork lift mode closely simulating the functionality of a heavy wooden or other comparable warehouse pallet. Since the warehouse pallets as may be used in conjunction with the lightweight pallets of the present invention are thus desirably limited to warehouse activities, but a limited number are required. Further, since the heavy pallets are not shipped, in addition to direct savings that are available from the inexpensive design of the pallets of this invention, significant weight reductions and space savings are also available to minimize shipping costs, and to maximize the amount of product shipped in the limited boxcar or truck trailer space.
The design features of the improved pallet, that contribute together to provide the utility described, include (a) a densely columnized raised platform, essentially the entire surface area of the platform, excepting the forked entry areas, bearing columns of critical sizing, height, and spacing patterns, (b) a stepped sidewall terminating in a rolled edge, (c) non-columnized spans for fork entry and retrieval that define balanced fork entry points, and (d) elongated ribs in the platform, out of phase, and cooperating with the column design and sidewall design to impart optimum utility traits to the pallet.
The pallet of the invention may also be designed to size itself to the lower geometry of the unitized load, without sacrificing the above properties. For these applications, the corner sections of the sidewall are trimmed away, creased, pleated, or otherwise suitably modified to permit inward load sizing movement of the sidewall. A critical radius is additionally designed at the base of the sidewall, permitting it to bend inwardly and flushly contact the base of the product load. The foregoing design is particularly useful for boxed, or unitized rectangular goods, rather than industrial bags, which tend to be self sizing, and thus have a lesser need for this latter feature.
In all cases referred to above, the pallet is designed for use in combination with a unitizing wrap, or wrap means, most frequently a stretch or shrink film overwrap, netting, or banding, which joins the load to the pallet. It is this feature with the described improved design features embodied in the pallet, which achieves the closely simulated utility characteristic vis-a-vis wooden and other heavy pallet structures. Since the latter typically have a pallet/load weight ratio of as little as 40-60, the advantages of the invention are thus readily apparent. Aside from the obvious weight savings and cost advantages, there are, of course, major savings permitted in the compact shipping of the inventive pallets in nested stacks, the washability of plastic as opposed to wood, the imperforate tray structure with optional imbiber bead fill to soak up and retain spillage, and the fact that the pallets of the invention may be economically reduced to scrap and reprocessed. Thus, collection and return of the inventive pallets (while feasible because of the nesting capability of the pallets) is not demanded by the economics.